Fix: (link) Don't match against null groups

e.g. in a source block containing Bash shell code like:

  [[ -z $data ]]

The matched groups could be null, since it's not actually an Org link,
so calling STRING-MATCH-P on them would signal an error.

Reported-by: John Wiegley <jwiegley@gmail.com>

README.org

@@ -555,7 +555,8 @@ Simple links may also be written manually in either sexp or non-sexp form, like:
 
 ** 0.8.10-pre
 
-Nothing new yet.
+*Fixes*
++ Predicate ~link~ could signal an error when searching text that is mistakenly recognized as an Org link (e.g. Bash double-bracket constructs in a source block).  (Thanks to [[https://github.com/jwiegley][John Wiegley]] for reporting.)
 
 ** 0.8.9
 

org-ql.el

@@ -1626,11 +1626,15 @@ any link is found."
                          (or (null description)
                              (string-match-p description (match-string org-ql-link-description-group)))))
               (_ (if (and description target)
-                     (and (string-match-p target (match-string 1))
+                     (and (and (match-string 1)
-                          (string-match-p description (match-string org-ql-link-description-group)))
+                               (string-match-p target (match-string 1)))
-                   (or (string-match-p description-or-target (match-string 1))
+                          (and (match-string org-ql-link-description-group)
-                       (string-match-p description-or-target
+                               (string-match-p description (match-string org-ql-link-description-group))))
-                                       (match-string org-ql-link-description-group)))))))))
+                   (or (and (match-string 1)
+                            (string-match-p description-or-target (match-string 1)))
+                       (and (match-string org-ql-link-description-group)
+                            (string-match-p description-or-target
+                                            (match-string org-ql-link-description-group))))))))))
 
 (org-ql-defpred (rifle smart) (&rest strings)
   "Return non-nil if each of strings is found in the entry or its outline path.

org-ql.info

@@ -1086,7 +1086,11 @@ File: README.info,  Node: 0810-pre,  Next: 089,  Up: Changelog
 5.1 0.8.10-pre
 ==============
 
-Nothing new yet.
+*Fixes*
+   • Predicate ‘link’ could signal an error when searching text that is
+     mistakenly recognized as an Org link (e.g.  Bash double-bracket
+     constructs in a source block).  (Thanks to John Wiegley
+     (https://github.com/jwiegley) for reporting.)
 
 
 File: README.info,  Node: 089,  Next: 088,  Prev: 0810-pre,  Up: Changelog
@@ -2093,50 +2097,50 @@ Node: Links38955
 Node: Tips39642
 Node: Changelog39966
 Node: 0810-pre40932
-Node: 08941047
+Node: 08941297
-Node: 08842191
+Node: 08842441
-Node: 08743267
+Node: 08743517
-Node: 08644495
+Node: 08644745
-Node: 08544729
+Node: 08544979
-Node: 08445385
+Node: 08445635
-Node: 08345837
+Node: 08346087
-Node: 08246178
+Node: 08246428
-Node: 08146571
+Node: 08146821
-Node: 0846994
+Node: 0847244
-Node: 07449720
+Node: 07449970
-Node: 07349945
+Node: 07350195
-Node: 07250679
+Node: 07250929
-Node: 07151600
+Node: 07151850
-Node: 0752411
+Node: 0752661
-Node: 06355277
+Node: 06355527
-Node: 06255810
+Node: 06256060
-Node: 06156117
+Node: 06156367
-Node: 0656687
+Node: 0656937
-Node: 05259743
+Node: 05259993
-Node: 05160045
+Node: 05160295
-Node: 0560470
+Node: 0560720
-Node: 04962001
+Node: 04962251
-Node: 04862283
+Node: 04862533
-Node: 04762632
+Node: 04762882
-Node: 04663041
+Node: 04663291
-Node: 04563449
+Node: 04563699
-Node: 04463810
+Node: 04464060
-Node: 04364169
+Node: 04364419
-Node: 04264372
+Node: 04264622
-Node: 04164533
+Node: 04164783
-Node: 0464780
+Node: 0465030
-Node: 03268881
+Node: 03269131
-Node: 03169284
+Node: 03169534
-Node: 0369481
+Node: 0369731
-Node: 02372781
+Node: 02373031
-Node: 02273015
+Node: 02273265
-Node: 02173295
+Node: 02173545
-Node: 0273500
+Node: 0273750
-Node: 0177578
+Node: 0177828
-Node: Notes77679
+Node: Notes77929
-Node: Comparison with Org Agenda searches77841
+Node: Comparison with Org Agenda searches78091
-Node: org-sidebar78730
+Node: org-sidebar78980
-Node: License79009
+Node: License79259
 
 End Tag Table